The present invention relates to a translucent projection screen for a rear-type image projection system used to observe the image from the side away from a projector and a method for manufacturing the same.
Translucent projection screens are used to view the image of an object projected on the rear surface and diffused to the front surface. They are widely used in rear projection type television receivers, rear-type slide projectors, rear-type microfilm readers and the like. The rear-type projection systems using translucent screens are simple in construction and operation and enable the projection of enlarged television pictures or images which may be clearly observed even in a lighted room. There are various types of translucent projection screens now available. For instance, they can be made of frosted glass; that is, from a glass plate whose surface is roughened mechanically or chemically. Some are made of plates of methacrylic resin whose surfaces are also roughened by a sand blasting process. Others are made of plates of synthetic resins in which light diffracting or reflecting materials are dispersed. Recently attempts have been made to combine a translucent projection system with a television receiver so as to enable the viewers to observe enlarged television pictures.
However, the use of the conventional translucent projection screens in projection television receivers has given rise to many difficult problems. The conventional translucent projection screens have been devised for and used in small-sized projection systems in which the enlargement of an object to be projected is small and a light source having a higher degree of luminance can be used. On the other hand, in the projection television receivers, the pictures focused on the face of a picture tube must be magnified or enlarged and projected on a screen. As a result the luminance of the projected pictures; that is, the screen gain is small. To overcome this problem, there has been devised and demonstrated a translucent projection screen having a Fresnel lens bonded or otherwise attached to one surface of the screen.
An important factor which affects the luminance of the projected pictures is the reflecting or diffusing characteristic of a screen used. Therefore, the conventional translucent projection screens have frosted or roughened or coated surfaces or are made of resins in which light diffusing materials are dispersed.